Guide
Skullcap side effects
Skullcap's most-reported side effects are drowsiness and dizziness; documented liver injury case reports exist for Chinese skullcap in a combination product and historically for American skullcap adulterated with germander.
The most-reported side effects of skullcap are drowsiness and, less often, dizziness. The more serious concern is liver injury — documented in case reports for Chinese skullcap in a combination product, and historically tied to American skullcap products adulterated with a genuinely toxic look-alike plant. This guide covers what's actually been reported for each species.
Drowsiness and dizziness
"Does skullcap make you sleepy" is one of the most common searches about this herb, and the honest answer from the controlled trial evidence is mixed. The 2014 randomized trial of American skullcap (350 mg, three times daily, two weeks) specifically reported no reduction in participants' energy or cognitive performance — the opposite of a sedating effect, at least in that trial's healthy adult sample. That doesn't rule drowsiness out for everyone; individual response to any herb varies, and case reports and product labels for skullcap commonly list drowsiness and dizziness as possible effects, particularly at higher intakes or in combination with other calming substances.
Liver injury: two separate stories, by species
Liver injury linked to "skullcap" shows up in the medical literature for two different reasons, depending on which species and which product:
- American skullcap and germander adulteration. Scutellaria lateriflora has historically been adulterated — sometimes accidentally through misidentification, sometimes through economic substitution — with germander (Teucrium canadense or T. chamaedrys), a plant that is itself directly hepatotoxic. A quality-control study using hyperspectral imaging and chemical analysis noted that cases of liver injury attributed to skullcap products have been linked to this kind of adulteration, and developed methods to detect germander mixed into skullcap raw material. The concern here is a contaminated or mislabeled product, not the correctly identified plant itself.
- Chinese skullcap in a combination supplement. Two published case reports describe patients who developed liver injury (elevated liver enzymes, jaundice) after taking a commercial joint-health supplement containing glucosamine, chondroitin, hyaluronic acid, and a proprietary extract combining Chinese skullcap with black catechu. In both reports, the injury resolved after stopping the supplement, and reviewers judged Chinese skullcap the most likely cause among the product's ingredients — though because it was one ingredient in a multi-ingredient formula, the case reports can't fully separate its effect from black catechu's.
Neither of these is a controlled trial measuring how often liver injury happens with skullcap; they're case reports, which describe what happened to specific people, not a rate that applies to everyone who takes the herb.
Questions people ask
Does skullcap make you sleepy?
Possibly, for some people — but the one controlled trial that measured it directly (350 mg, three times a day) found no reduction in energy or mental performance. Individual responses vary, and drowsiness is commonly listed as a possible effect on product labels regardless of what that one trial found.
Can skullcap cause liver damage?
Yes, in specific documented cases — see the liver injury section above. American skullcap's cases have generally traced back to adulteration with a toxic look-alike plant, not the correctly identified herb; Chinese skullcap has case reports tied to it directly, though in a combination product. Anyone with existing liver problems should talk to a doctor before taking either species.
Can skullcap make you dizzy?
Dizziness is commonly listed as a possible side effect on skullcap product labels and in case reports, though it hasn't been measured as a specific outcome in the controlled human trials that exist.
Will skullcap enhance the effects of a sleep medication?
That combination hasn't been tested in a trial. Because skullcap is traditionally used as a calming herb, combining it with a sedative or sleep medication is a reasonable thing to ask a doctor or pharmacist about before doing — see skullcap and medications: what to check.
Related reading: who should not take skullcap, skullcap and medications: what to check, and how to choose a good skullcap.
Sources
- Skullcap and germander: preventing potential toxicity through the application of hyperspectral imaging and multivariate image analysis as a novel quality control method A plant-quality-control study noted that liver injury cases attributed to skullcap products have been linked to adulteration with germander, a toxic look-alike plant, and developed lab methods to detect it.
- Hepatotoxicity associated with chinese skullcap contained in Move Free Advanced dietary supplement: two case reports and review of the literature Two case reports found liver injury in patients taking a joint-health supplement containing Chinese skullcap combined with black catechu; the injury resolved after stopping the product, and Chinese skullcap was judged the most likely cause.
- Herbal hepatoxicity from Chinese skullcap: A case report A case report describes a patient whose liver injury from a Chinese skullcap-containing joint supplement resolved after stopping it, then recurred when she restarted the same product, confirming the link in that individual.
- American Skullcap (Scutellaria lateriflora): a randomised, double-blind placebo-controlled crossover study of its effects on mood in healthy volunteers A 2014 randomized trial found no significant difference between American skullcap and placebo on a standard anxiety scale, though a separate mood measure improved; the trial had carryover and baseline-imbalance limitations.
*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.