Guide
Forskolin (Coleus forskohlii) side effects
The two existing 12-week human trials on oral forskolin extract found no clinically significant changes in blood chemistry, liver or muscle enzymes, blood counts, hormones, heart rate or blood pressure. A pharmacology review separately flags a possible increase in stomach acid as a mechanism-based caution.
The two existing 12-week human trials on oral forskolin extract found no clinically significant changes in safety bloodwork, heart rate, or blood pressure compared with placebo. Neither trial lists a specific rate for common complaints like stomach upset or headache — both simply report nothing clinically significant to flag. A separate pharmacology review adds one mechanism-based caution worth knowing: a possible increase in stomach acid.
What the trials actually monitored
A 2005 trial in 30 overweight or obese men tracked body composition and hormone changes over 12 weeks of 250 mg of a 10% forskolin extract, twice a day; its published abstract doesn't report a separate side-effect or adverse-event tally beyond those outcomes (PMID 16129715). A second 2005 trial, in mildly overweight women using the identical extract and dose, specifically tracked side effects on a weekly basis and reported no clinically significant differences from placebo across metabolic markers, blood lipids, liver and muscle enzymes, electrolytes, blood cell counts, hormones, heart rate, or blood pressure over the same 12 weeks (PMID 18500958). That's the most detailed safety monitoring that exists for the oral capsule form, and it came back clean on the measures it checked.
What was reported, not measured as an "adverse" event
In the women's trial, people taking forskolin reported less fatigue, less hunger and less fullness than the placebo group — subjective, self-reported measures rather than documented side effects, and not something the trial framed as a benefit either (PMID 18500958). It's included here because it's the kind of day-to-day experience people ask about, not because it was studied as an outcome in its own right.
Stomach acid: a mechanism-based caution
A 2012 pharmacology review of forskolin's research as a glaucoma candidate describes forskolin as potentially raising stomach acid levels, based on its underlying pharmacology rather than a side-effect count from a trial, and flags a caution around combining it with medications for stomach ulcers (PMID 23023353). If you have a history of ulcers or acid reflux, that's worth knowing, and worth a conversation with a doctor before adding forskolin. See forskolin and medications: what to check and who should not take forskolin? for more.
What this page doesn't cover
Forskolin's other researched forms — eye drops for eye pressure, a modified water-soluble version studied for the heart — weren't tested as an oral capsule, so their effects (and any side effects specific to those forms) don't apply here. See forskolin benefits: what the research does and doesn't show for that research.
Questions people ask
What are the side effects of forskolin?
The two existing human trials on the oral capsule found no clinically significant changes in safety bloodwork, heart rate, or blood pressure over 12 weeks. Neither trial's published results list a specific rate for milder complaints like stomach upset.
Does forskolin affect the heart?
Both existing trials measured heart rate and, in one case, blood pressure, with no clinically significant change reported versus placebo over 12 weeks. Separately, a pharmacology review notes forskolin's mechanism can act on heart tissue in laboratory research, which is a reason to ask a doctor before combining it with any heart medication — see forskolin and medications: what to check.
Can forskolin cause an upset stomach?
Neither trial reported a specific rate for this, but a pharmacology review notes forskolin may raise stomach acid, which is a plausible reason some people notice stomach upset, particularly on an empty stomach.
Is forskolin safe?
In the two existing 12-week trials, it produced no clinically significant changes in a fairly wide panel of safety bloodwork, heart rate, or blood pressure. That's a limited base of evidence — two small trials — not a guarantee for everyone, especially anyone on medication or with an existing health condition. See who should not take forskolin?
Related reading: who should not take forskolin?, forskolin and medications: what to check, and how much forskolin should you take a day?
Sources
- Body composition and hormonal adaptations associated with forskolin consumption in overweight and obese men A 2005 trial in 30 overweight or obese men used 250 mg of a 10% forskolin extract, twice a day, for 12 weeks — the standardization and dose referenced elsewhere on this site.
- Effects of coleus forskohlii supplementation on body composition and hematological profiles in mildly overweight women A 2005 trial in mildly overweight women used the identical extract and dose as the men's trial: 250 mg of a 10% forskolin extract, twice a day, for 12 weeks.
- Forskolin: upcoming antiglaucoma molecule A 2012 review of forskolin as a glaucoma research candidate describes its cAMP-based mechanism for lowering eye pressure, tested topically as drops rather than as an oral supplement.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.