Drink-driving: the 50mg and 20mg limits, refusal, and the real penalties

Driving while drunk is prohibited by section 43(2) of the Road Traffic Act B.E. 2522 (1979). The limits sit in Ministerial Regulation No. 21 (B.E. 2560, 2017): over 50 milligram-percent blood alcohol counts as drunk for ordinary licence holders, but the threshold drops to just 20 milligram-percent — roughly one drink — for drivers under 20 years old, holders of a temporary (first two-year) licence, and anyone driving with no licence or a suspended or revoked one. New arrivals on a fresh Thai licence are in the 20mg group and rarely know it.

Officers with reasonable grounds may order a test (s. 142); refusing without reasonable justification means you are legally presumed drunk, and you can be detained until testing is completed. Penalties under section 160 ter: up to one year imprisonment or a 5,000–20,000-baht fine or both, plus licence suspension of at least six months. The 2022 amendment (Road Traffic Act No. 13, in force 5 September 2022) added a repeat-offender rule: a second offence within two years carries up to two years imprisonment AND a 50,000–100,000-baht fine — the court must impose both — with at least one year's suspension. Causing injury raises it to 1–5 years; serious injury 2–6 years; death 3–10 years with a 60,000–200,000-baht fine and permanent revocation.

A drunk-driving offence also deducts four demerit points, and the standard voluntary motor policy excludes your own-damage cover above these same limits.