Yes but medication is not safe and is yet to be approved by FDA.
Invalid means either the test is negative or sample was too less to give out any result.
Hormones released during pregnancy such as progesterone keeps the mood right. However, post pregnancy there is a sudden drop in the hormone progesterone which results in post partum depression.
If a man uses a rapid antigen pregnancy test the test will be negative. However, research is suggestive that if the test is positive (remote possibility) then he should consult a doctor right away to investigate prostrate-related conditions.