THC-Nachweisrechner

Active THC (Δ9-THC) reaches the bloodstream within minutes after smoking. Plasma half-life is around 1–4 hours after a single use, but the THC stored in body fat is released slowly over days or weeks. The metabolite THC-COOH (carboxy-THC) has a half-life of 1–6 days for occasional users and up to 5–13 days for chronic users. That is why heavy users can still test positive weeks after their last use, while occasional users are usually clean within 3–7 days.

Since the German Cannabis Act (KCanG, in force 22 August 2024), driving with 3.5 ng/mL or more active THC in blood serum is an administrative offence under § 24a para. 1a StVG. Previously, courts treated the analytic detection threshold of 1.0 ng/mL as the legal limit. The new value matches the level at which a measurable impairment of driving fitness is empirically expected. Combining cannabis with alcohol remains strictly forbidden — there is effectively a 0.0 limit for mixed consumption.

An MPU can be ordered after: a single offence above the 3.5 ng/mL THC limit, repeated offences, or proof of habitual cannabis use combined with traffic infringements. The assessor will classify under one of four hypotheses (D1–D4). For most cases an abstinence proof of 6–12 months is required (urine programme, hair analysis or both). Hypothesis D4 demands proof of separation between use and driving, not full abstinence. For the full picture after KCanG see our Cannabis & MPU 2024 hub.

• ·Legal possession does not protect your driving licence — the 3.5 ng/mL limit still applies fully.
• ·Plan at least 8–12 hours between last use and driving for occasional users; daily users should not drive at all without a clean blood test.
• ·Body fat retains THC — leaner bodies eliminate faster. The slider in the calculator reflects this roughly.
• ·Hair tests can detect cannabis use across the past 3–6 months. Cosmetic dyes or bleach do not reliably mask it.