Almost all laboratory animals can be restrained safely and humanely provided they are handled correctly. All animals benefit from being first accustomed to being handled, and this can be done during the period of acclimatisation needed before they are used on a research procedure.
It has been shown that picking up mice by the tail induces aversion and high levels of anxiety. (Hurst & West 2010*) Using tunnels or cupping the mice in open hands leads to more rapid acceptance of physical restraint. Habituation to this type of initial restraint persists even when mice are subsequently restrained more securely, for example by the scruff to allow injections to be carried out.
If injections are to be repeated on a regular basis, then familiarization with restraint assumes even greater importance, and training of the animal to co-operate with the procedure may also be helpful.
If you are relatively inexperienced in the technique that you plan to use, you should ensure you have an experienced assistant who can restrain the animal safely and humanely, and assist and supervise the procedure.
When carrying out procedures, make sure you are wearing appropriate protective clothing, both to protect yourself from hazards such as allergens, and to protect the animal from inadvertent transfer of potential infectious agents.