Acarbose (Precose) is an alpha-glucosidase inhibitor — a small group of drugs that block the intestinal enzymes that break down complex carbohydrates into absorbable sugars. The result is a flatter, smaller glucose rise after meals. A1C drops are modest at 0.5 to 0.8 percent, the drug is weight-neutral, and hypoglycemia is rare alone. The trade-off is gastrointestinal side effects — flatulence, bloating, diarrhea — that affect most users initially but usually improve over weeks. Acarbose also has a documented role in prediabetes prevention through the STOP-NIDDM trial.
How Acarbose Works
Acarbose binds reversibly to alpha-glucosidase enzymes (sucrase, maltase, glucoamylase, dextrinase) at the brush border of the small intestine. These enzymes normally cleave complex carbohydrates and disaccharides into absorbable monosaccharides. With acarbose on board, the breakdown is delayed — carbohydrate digestion and glucose absorption are spread further down the small intestine. The net effect is a lower and later post-meal glucose peak.
- Drug class: alpha-glucosidase inhibitor
- Brand name: Precose (US), Glucobay (most of world)
- Generic status: yes
- Onset: with the first dose (mechanical, not systemic)
- Systemic absorption: very low (less than 2 percent absorbed intact)
- Excretion: about 50 percent fecal (unabsorbed), 35 percent renal (absorbed fraction)
Approved Uses
- Adjunct to diet and exercise in adults with type 2 diabetes
- Monotherapy or combination with metformin, sulfonylureas, or insulin
- Off-label use in prediabetes prevention (more common in Europe and Asia)
- Not used in type 1 diabetes or diabetic ketoacidosis
Typical Dosing
| Phase | Dose | Schedule |
|---|---|---|
| Starting | 25 mg once daily | With the first bite of one main meal |
| Week 2 to 4 | 25 mg three times daily | With first bite of each main meal |
| Week 4 to 8 | 50 mg three times daily | With first bite of each main meal |
| Maintenance | 50 to 100 mg three times daily | With first bite of each main meal |
| Maximum (less than 60 kg) | 50 mg three times daily | — |
| Maximum (more than 60 kg) | 100 mg three times daily | — |
Slow titration is essential to manage GI side effects. The first dose of the day should be at breakfast — taking the drug without a meal provides no benefit because the enzyme inhibition needs carbohydrate to act on.
Effect on Glucose and A1C
- A1C reduction: 0.5 to 0.8 percent — modest compared with metformin or sulfonylureas
- Post-meal glucose: 30 to 50 mg/dL reduction at peak effect
- Fasting glucose: minimal direct effect (drug works on food, not basal)
- Weight: neutral (sometimes a small loss)
- Lipids: small reductions in triglycerides
- Cardiovascular: STOP-NIDDM and ACE trials suggested possible CV event reductions, though absolute effect is modest
The STOP-NIDDM Trial
The STOP-NIDDM trial (Chiasson et al., Lancet 2002) randomized 1,429 patients with impaired glucose tolerance to acarbose or placebo, with a mean follow-up of 3.3 years. Key findings:
- Acarbose reduced the relative risk of progression to type 2 diabetes by 25 percent
- The absolute risk reduction was approximately 9 percentage points (32 percent of acarbose group versus 42 percent of placebo group)
- Cardiovascular events were reduced by 49 percent (smaller numbers, wide confidence interval, but consistent direction)
- Discontinuation was higher in the acarbose arm because of GI side effects
STOP-NIDDM established acarbose as one of the few drugs with documented benefit in preventing progression from prediabetes to type 2 diabetes, alongside metformin (DPP study) and intensive lifestyle change.
Common Side Effects
| Side Effect | Frequency | Notes |
|---|---|---|
| Flatulence | Up to 60% initially | Usually improves over 4 to 12 weeks |
| Diarrhea | 30 to 40% | Dose-related; improves with adaptation |
| Abdominal pain or cramping | 20% | Dose-related |
| Bloating | Frequent | Dose-related |
| Hypoglycemia (alone) | Rare | Common when combined with SU or insulin |
| Elevated liver enzymes | 3 to 4% at high doses | Usually reversible; check LFTs every 3 months in first year |
Serious but Less Common Side Effects
- Hepatitis or jaundice — rare, especially at doses above 300 mg/day; reversible on stopping
- Ileus, intestinal obstruction symptoms — rare; investigate persistent severe abdominal pain
- Pneumatosis cystoides intestinalis — rare; gas pockets in bowel wall
- Allergic skin reactions — rare
- Anemia from iron malabsorption — rare
- Reduced absorption of digoxin and other drugs — separate dosing
Treating Hypoglycemia on Acarbose Combos
If a patient on acarbose plus a sulfonylurea or insulin develops hypoglycemia, the standard 15 g of carbohydrate must come from pure glucose, not sucrose:
- Use: glucose tablets, glucose gel, fruit juice (orange, apple — contain glucose and fructose), milk (lactose)
- Avoid: table sugar, hard candies sweetened with cane sugar, syrup, soda with sucrose (acarbose blocks sucrose breakdown)
- Severe hypoglycemia: IM glucagon or IV dextrose; emergency care
- Teach household members about this distinction
Who Should Not Take Acarbose
- Inflammatory bowel disease (Crohn’s, ulcerative colitis)
- Chronic intestinal disorders with malabsorption or significant flatulence
- Significant liver disease
- Severe kidney disease (eGFR <25 mL/min)
- Diabetic ketoacidosis or type 1 diabetes
- Cirrhosis
- Known hypersensitivity
- Pregnancy and breastfeeding (limited data)
Drug Interactions
- Digoxin — acarbose may reduce digoxin levels; monitor
- Pancreatic enzyme supplements — antagonize acarbose effect; avoid co-administration
- Intestinal adsorbents (cholestyramine) — antagonize effect
- Sulfonylureas and insulin — increased hypoglycemia risk
- Sulfonylureas alone — additive A1C reduction without increased hypoglycemia from acarbose itself
- Acarbose does not significantly interact via cytochrome P450 because it is not appreciably absorbed
Acarbose Compared with Other Add-On Classes
| Class | A1C Drop | Weight | Hypo Alone | Main Side Effects | Cost/Month |
|---|---|---|---|---|---|
| Acarbose | 0.5 to 0.8% | Neutral | Rare | GI — flatulence, diarrhea | ~$15 to $50 generic |
| Metformin | 1.0 to 1.5% | Neutral or loss | Rare | GI upset, B12 deficiency | ~$4 |
| Sulfonylureas | 1.0 to 1.5% | +2 to 5 kg | Common | Hypoglycemia, weight gain | $4 to $15 |
| DPP-4 inhibitors | 0.5 to 0.8% | Neutral | Rare | Generally well tolerated | $500 to $700 |
| SGLT2 inhibitors | 0.5 to 1.0% | -2 to 4 kg | Rare | GU infection, DKA risk | $500 to $700 |
| GLP-1 agonists | 1.0 to 2.0% | -4 to 15 kg | Rare | GI upset | $500 to $1,300 |
Other Drugs in the Alpha-Glucosidase Inhibitor Class
- Miglitol (Glyset) — similar mechanism with slightly different absorption (partially absorbed systemically); A1C drops 0.5 to 0.8 percent; similar GI side-effect profile; not widely used in the US
- Voglibose — used in Japan and parts of Asia; not FDA-approved
Where Acarbose Fits in 2024 Care
The ADA Standards of Care 2024 list alpha-glucosidase inhibitors as one of several add-on options, particularly for post-meal glucose excursions. Use is uncommon in the US because of the modest A1C effect and high GI side-effect burden. Acarbose is more widely used in:
- Asia, particularly East Asia, where diets are higher in carbohydrate and post-meal glucose excursions are pronounced
- Europe
- Settings where cost limits access to newer drugs
- Prediabetes prevention as an alternative to or addition to metformin
- Patients in whom hypoglycemia is a particular concern (acarbose monotherapy almost never causes it)
Practical Tips
- Take the tablet with the very first bite of your meal — not after
- Start at 25 mg once daily and increase slowly over weeks
- Eat a balanced, moderate-carbohydrate diet; avoid large carbohydrate boluses, which worsen GI side effects
- Stay hydrated
- Keep glucose tablets, juice, or milk for hypoglycemia — never rely on table sugar if also on insulin or a sulfonylurea
- Track GI symptoms; they usually improve over 1 to 3 months
- Get baseline liver function tests; recheck every 3 months in the first year
- Tell every clinician you take acarbose, especially before any procedure requiring fasting
Acarbose for Prediabetes
STOP-NIDDM was a landmark — acarbose joined metformin and intensive lifestyle change as the only therapies with documented reduction in progression from prediabetes to type 2 diabetes in randomized trials. In US practice, lifestyle change and metformin are usually tried first. Acarbose is reasonable when:
- Metformin is not tolerated
- Post-meal glucose excursions are the dominant pattern
- Hypoglycemia concern argues against secretagogue-based approaches
- Patient preference and willingness to manage GI side effects
Related Reading
See our broader treatment overview, A1C levels guide, is prediabetes reversible, and our diet and nutrition articles — diet matters even more when the drug’s mechanism is to modify carbohydrate absorption. The class-level sulfonylureas side effects guide is useful when acarbose is combined with a secretagogue.
The Bottom Line
Acarbose (Precose) is a niche but useful diabetes drug. It blocks intestinal alpha-glucosidase enzymes, blunts post-meal glucose spikes, and produces a modest 0.5 to 0.8 percent A1C drop. The drug is weight-neutral, rarely causes hypoglycemia alone, and has documented benefit in preventing progression from prediabetes to type 2 diabetes (STOP-NIDDM). The dominant side effect is gastrointestinal — flatulence, bloating, diarrhea — and these often improve over weeks with slow titration. Use is uncommon in the US compared with Asia or Europe. If hypoglycemia occurs in a combination regimen, treat with pure glucose, not table sugar. Talk to your clinician about whether acarbose fits your situation, particularly if post-meal glucose excursions are dominant or if hypoglycemia must be avoided.
