Regulation 4 ProhibitionsI1 Northern Ireland Subject to regulation 5, no person shall— (a) add tryptophan to food; (b) sell, or offer for sale, food containing tryptophan; or (c) expose for sale food containing tryptophan. Annotations Commencement I1 Reg. 4 in operation at 11.11.2005, see reg. 1 ← Regulation 3 Regulation 4 Regulation 5 →