Usually give something a bottle or two, depending on daily amounts, before deciding if it's worth continuing. Tried a full ss31 run once, wasn't impressed.
As for reta, 2mg hit like a truck initially, and the effect's shifted over time, especially now training harder. Appetite suppression feels weaker lately but the near-total absence of food noise remains, plus fullness kicks in faster. Weekly Monday shots mean by Saturday the effects noticeably fade. Titrating to 4mg brought serious constipation, genuinely rough. Down 43 pounds but stalled recently.
Meanwhile a family member barely eats, zero noticeable sides. More dose for them doesn't add more side effects either, just steady loss, no constipation.
Short version, give it a real chance before writing it off.