Tetracyclin was passed out like candy in the 60's and 70's so there are, IIRC, many bugs resistant to it and that makes it a mixed value.
Phenergan, aka promethazine, is IIRC part of the "NASA cocktail" and a strong antihistamine. Many antihistamines are used to prevent seasickness, all can make you drowsy, and like most good drugs it has a list of side effects:
"Drowsiness is the most prominent CNS effect of this drug. Extrapyramidal reactions may occur with high doses; this is almost always responsive to a reduction in dosage. Other reported reactions include dizziness, lassitude, tinnitus, incoordination, fatigue, blurred vision, euphoria, diplopia, nervousness, insomnia, tremors, convulsive seizures, oculogyric crises, excitation, catatonic-like states, and hysteria."
All the more reason to have several meds in the kit, rather than just one. And, to actually try them out while at home, on land, with a "trip sitter" to keep an eye on you. Just in case.