See our birth control comparison for the full effectiveness picture — the implant is one of the most effective reversible methods available, on par with IUDs, while the shot's typical-use effectiveness is noticeably lower specifically because it requires repeat action to stay effective.
The implant
A small, flexible rod inserted under the skin of the upper arm by a healthcare provider, releasing progestin steadily over time. Once placed, it requires no ongoing action at all — nothing to remember daily, weekly, or monthly — which is exactly why its typical-use and perfect-use effectiveness are essentially the same, both under 1%. It's commonly approved for around 3 years depending on the specific product, though it can be removed earlier by a provider at any time if someone changes their mind.
The shot
An injection, administered by a healthcare provider (or in some cases self-administered with training), that needs to be repeated on a set schedule — commonly every few months — to remain effective. Unlike the implant, this repeat-action requirement creates a real gap between perfect-use effectiveness (under 1%) and typical-use effectiveness (around 4%), since missing or delaying a scheduled dose reduces protection.
Being progestin-only matters for some people
Because neither contains estrogen, both can be reasonable options for people who can't or shouldn't use estrogen-containing methods for health reasons — worth discussing directly with a doctor, since that's a genuine medical distinction from the combined methods covered in our guide to the pill, patch, and ring.
Common side effects to know about
Irregular bleeding patterns are common with both, especially in the first several months, and can include spotting, longer or shorter periods, or periods stopping altogether for some people. Weight change has been reported by some users of the shot specifically, though research on how consistent this effect actually is has produced mixed results — worth raising directly with a prescriber rather than assuming one way or the other.
Frequently asked questions
Why is the implant more effective in typical use than the shot?
The implant requires no ongoing action after insertion, while the shot needs to be repeated on schedule (commonly every few months) to stay effective — that repeat-action requirement is exactly the kind of gap that creates a difference between typical and perfect use.
Does the shot cause weight gain?
Some people report weight gain while using it, though research on how consistent or significant this effect is has produced mixed results, and individual response varies. It's a reasonable question to raise directly with a prescriber when weighing options.
How long do these last?
The implant is commonly approved for around 3 years depending on the specific product, though it can be removed earlier at any time. The shot requires repeat injections on a set schedule, commonly every few months, to remain effective — it isn't a one-time long-term method the way the implant is.
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