THCA is a non-intoxicating cannabinoid found in high levels in the marijuana form of the cannabis plant. Smaller quantities are often also found in the hemp form of cannabis. In the U.S. hemp is defined as any cannabis containing over 0.3% delta-9 THC. The THCA content doesn’t count (according to most interpretations of the 2018 Farm Bill). In the E.U. hemp must have 0.2% delta 9 THC or less.
Approximately 85% of THCA converts into delta 9 THC when it is vaped or smoked. Juicing raw cannabis or using it as a tea are ways of taking THCA. You just have to keep it below 220 degrees F. to prevent it from converting to THC.
Like some other cannabinoids THCA appears to be neuroprotective and it has been used to treat seizures. It has been found to have some anti-cancer activity, but it has not been studied as much as CBD and THC for this. It is an anti-inflammatory and may help arthritis pain.
THCA is federally legal in the U.S. and internationally; but it usually co-occurs with THC which is often illegal.
THCA can be used medically at quite low doses, according to Project CBD.