To understand why the Botox comparison falls apart, you need the actual mechanism of each.
Botulinum toxin is injected directly into a facial muscle. There it blocks a set of proteins nerves use to release acetylcholine, the chemical messenger that tells muscle to contract. No messenger, no contraction, and the overlying skin stops creasing. It works because it is delivered into the tissue that needs to change.
Argireline was designed to interfere with the same protein complex. In a laboratory dish, it does. The trouble is everything between the bottle and the muscle. A facial muscle sits under the full thickness of the skin and the fat beneath it. A peptide applied to the surface has to cross the outer barrier, then the epidermis, then the dermis, in enough quantity to matter. Peptides are large and water-loving, which is close to the worst combination for getting through skin. Very little arrives, and there is no good demonstration that a meaningful amount reaches a muscle.
So what do the studies that show something actually show? Small reductions in the appearance of fine lines, measured over weeks. Those results are consistent with hydration, surface smoothing and possibly a very local effect in the skin — not with muscle relaxation. That is the honest reading.
Argireline is a real ingredient with a plausible laboratory mechanism and a delivery problem nobody has solved. Calling it topical Botox is not a scientific claim. It is a way of borrowing a famous name.
Argireline is very well tolerated. Side effects are uncommon and mild.
There is no group that must avoid argireline for safety reasons. It is a mild cosmetic peptide with no meaningful systemic absorption and no known serious risks from topical use.
Avoid it if you have reacted to it or to a product containing it before.
In pregnancy and breastfeeding, topical peptides are generally regarded as low concern, and argireline is one of the things people use in place of a retinoid. Specific safety data are limited, so that is an absence of known problems rather than positive evidence. The rest of the formula deserves more attention than the peptide.
The more useful question is who should not bother buying it. If you want the effect that botulinum toxin produces, no topical product delivers it, and Botox is what you are actually describing. If your lines are visible at rest, they are structural and a serum will not remove them. And if you are paying a premium for a product whose main claim is the Botox comparison, you are paying for the comparison.
Everyone else can use it. It is harmless, cheap and mild, and it is fine as one part of a routine as long as nobody has promised you more than that.
Two weeks. Some people report skin looking a little smoother. Much of this is hydration from the serum base, and some products add film formers that tighten skin for a few hours after application.
Four to eight weeks. The window in which the available studies report small reductions in the appearance of fine lines. Small means detectable by measurement and easy to miss in the mirror.
Three months. About as far as the evidence goes. Whatever effect you get, you have it by now.
There is no point at which movement stops or expression lines disappear. That does not happen with a topical peptide, at any concentration, over any timeframe.
When you stop. Any effect fades within weeks, and the hydration component goes as soon as you stop applying it. Compare that with Botox, where a single treatment lasts three to four months — a difference in kind, not degree.