How to take Tresiba. Tresiba is injected under the skin. You will be shown how to use injections at home. Do not give yourself Tresiba if you do not understand how to use the injection and properly dispose of used needles and syringes. Tresiba must not be given with an insulin pump, or mixed with other insulins. Do not inject insulin into a vein or a muscle. Tresiba is usually given once daily, at any time of the day. Follow your doctor’s dosing instructions very carefully.