Short answer: Bacopa has more trials behind it: a meta-analysis of 9 trials (518 people) found faster attention scores after at least 12 weeks.1 Lion's mane has a few small trials, including 30 older adults with mild cognitive impairment whose gains faded after stopping, and mostly null results in young adults.23 No trial compared them.
| Lion's mane | Bacopa | |
|---|---|---|
| What it is | Edible mushroom Hericium erinaceus2 | Bacopa monnieri, an Ayurvedic plant1 |
| Largest evidence | Small trials, such as 30 and 41 people23 | Meta-analysis of 9 trials, 518 people1 |
| Key finding | 16 weeks in mild cognitive impairment: better scores vs placebo, which fell after stopping2 | Faster Trail B and choice reaction time vs placebo1 |
| Healthy adults | 28 days in 41 young adults: mostly null3 | 12 weeks in 54 adults 65+: better delayed word recall4 |
| Study amounts | 1.8 g a day for 28 days3 | 300 mg a day of standardized extract4 |
| Side effects reported | Dropouts for stomach discomfort, nausea or rash in one trial5 | Mostly stomach upset, 9 on bacopa vs 10 on placebo4 |
Lion's mane: in 30 Japanese adults aged 50 to 80 with mild cognitive impairment, 16 weeks of dried mushroom tablets raised thinking scores more than placebo; scores dropped within 4 weeks of stopping.2 A 49-week pilot in mild Alzheimer's disease used a mycelium product and reported better scores than placebo.5 In 41 healthy adults aged 18 to 45, the results were mostly null, with faster scores on one test after a single dose.3
Bacopa: a 2014 meta-analysis of 9 trials of standardized extracts taken for at least 12 weeks found faster attention test times than placebo, and said a large head-to-head trial is needed for firm answers.1 In 54 adults aged 65 and over, 300 mg a day for 12 weeks improved delayed word recall.4
Bacopa trials measured effects after weeks of daily use, not single doses. These are study protocols, not personalized advice; confirm any dosing with your prescriber.
Products differ a lot: lion's mane is sold as fruiting body or mycelium, and bacopa extracts differ in strength. Authors of two lion's mane trials worked for mushroom product companies.25 Neither is approved by FDA before sale.6
More detail: Alpha-GPC vs citicoline: how do these choline sources differ?, Piracetam vs aniracetam: what is known about each?, and the Lion's Mane (Hericium erinaceus) and Bacopa Monnieri guides.