tDCS and tACS: Educational Overview and Risks

Safety first: this page gives no device settings, electrode placements or build instructions, and it never will. Making or modifying a stimulator at home can burn skin and affects the brain in ways that are not well understood. Read DIY brain stimulation risks before considering anything of the kind.

What tDCS and tACS are

Transcranial direct current stimulation (tDCS) passes a weak, steady electrical current between electrodes on the scalp. The FDA describes a tDCS device as one that delivers low-intensity direct electrical current to specific areas of the brain via electrodes placed on the scalp. [1] Transcranial alternating current stimulation (tACS) uses an alternating current. Both are studied in clinics and laboratories, and the technology is covered in more depth in tDCS and tACS: research evidence.

Evidence labels used here: approved medicine (with the regulator and indication), promising but limited, mixed, insufficient evidence, no good evidence of benefit and marketing claim.

Regulatory status in the United States

• Approved use. On December 8, 2025, FDA approved one headset, the Flow FL-100, through premarket approval (PMA P230024). FDA lists it as a "cranial electrotherapy stimulator to treat depression" under regulation 882.5800. [2] The approval order says it is intended for moderate to severe major depressive disorder in the current episode, alone or as an add-on, in adults 18 and older who are not considered treatment refractory to medication. [2] Label: approved medicine for that specific indication only.
• FDA's own caveat. In FDA's evaluation, there is a moderate level of uncertainty of benefit due to unblinding, among other issues. [1]
• Everything else. An approval for one device and one use is not approval of tDCS in general. A 2015 legal analysis explains that what decides whether a product is regulated as a medical device is its intended use rather than how it works. [3] That analysis is a decade old and United States only; I did not verify today's market or rules. Laws change and this is not legal advice.

What research shows

Remember that "better than sham" in a small trial is not the same as proof of a lasting daily-life benefit.

Risks and side effects

• Common. In the approved headset's trial, skin redness (63.5% vs 18.5% with sham) was the most frequent problem. [1] FDA's list of potential adverse effects also includes skin burn, headache, tinnitus, and acute mood change or worsening depression. [1]
• Persistent events. A review of tDCS and tACS reports found skin lesions similar to burns, which can arise even in healthy people, and mania or hypomania in patients with depression. It also notes there are no formal safety guidelines for the selection of stimulus parameters. [9]
• Reassuring research data. A 2016 evidence review found that conventional protocols in human trials had not produced any reports of serious adverse effect across more than 33,200 sessions. [10] Those were supervised research settings. A review of repeated sessions concluded that higher risks from more exposure, or rare and under-reported events, cannot be ruled out. [11]
• Children and teens. The pediatric safety evidence is sporadic and scarce. [12]
• Contraindications named by FDA for the approved headset. Open wounds or damaged skin at the electrode site, and metallic skull reconstruction at the electrode site. [1]

Who should not experiment, and who should talk to a clinician first

People with epilepsy or past seizures, bipolar disorder or a history of mania, implants, skin damage on the scalp, or any psychiatric condition should not try stimulation on their own. For children and teens, ask a pediatric clinician; the evidence is thin. See brain stimulation contraindications and seizure considerations and talking with a health professional. If you are in crisis, call or text 988 (US Suicide & Crisis Lifeline).

How to evaluate claims

Ask which condition was studied, whether there was a sham group, whether the stimulation matched what a product actually delivers, and who funded the work. See clinical vs consumer brain stimulation devices and electrical stimulation risks.