That includes when using weight loss supplements! Once you start supplementing your body, your body needs to build up the supplements in your system so that they can take full effect.
If you take the supplements for a week and you forget about them for a month, then decide to come back to using them, you will not receive the same kind of results as if you stayed on the supplements for the duration of the bottle as the directions state. Follow the directions on the label and be sure to drink plenty of water!