"diminish the effectiveness" is a correct and usable phrase in written English.
This phrase can be used to indicate that something is decreasing in its ability to be successful or its impact. For example, "The lack of resources has diminished the effectiveness of the program."
According to The Mayo Clinic, while alcohol won't necessarily diminish the effectiveness of antibiotics, it can cause side effects.
Potential hazards include an increased risk of falls and vehicular accidents, a decline in short-term memory, a worsening of existing health problems and interactions with medications that may diminish the effectiveness of some drugs and increase the toxic effects of others.
Conversely, alcohol may diminish the effectiveness of drugs and even worsen symptoms.
These reforms not only make voting easier, they also reduce congestion at polling places on Election Day and diminish the effectiveness of last-minute negative political attacks.
To many, the statement Times Square now makes is, "All right, already!" as the many new signs on new buildings contribute to a cacophony that seems to diminish the effectiveness of each billboard.
He said the groups challenging the law feared that "adopting a policy explicitly opposing prostitution may alienate certain host governments, and may diminish the effectiveness of some of their programs by making it more difficult to work with prostitutes".
In particular, the immediate paradoxical aftereffect, interpreted by us as a rebound effect, diminishes the effectiveness of sustained regulation.
Public colleges organized as systems also developed effective strategies, although bureaucratic guidelines sometimes diminished the effectiveness of central office mandates.
It diminishes the effectiveness of America's role as "honest broker" in the Mideast dispute.
"Bribery diminishes the effectiveness of law enforcement, particularly where punishment of crimes relies on evidence from the victim.
Justice Samuel Alito Jr. wrote that the rule diminished "the effectiveness" of the rich candidate's spending and of his speech.
