The phrase 'diminished the effectiveness' is correct and usable in written English.
You can use this phrase to refer to a situation in which something is not as effective as it could have been. For example: "The strong winds diminished the effectiveness of the sailboat's journey."
Public colleges organized as systems also developed effective strategies, although bureaucratic guidelines sometimes diminished the effectiveness of central office mandates.
Justice Samuel Alito Jr. wrote that the rule diminished "the effectiveness" of the rich candidate's spending and of his speech.
She observed that when AMPK was paired with cisplatin at the beginning of treatment the combination diminished the effectiveness of cisplatin.
In the '80s and '90s, however, Congress diminished the effectiveness of the program by eliminating the national trigger, raising the state triggers and altering the trigger calculations in such a way that they hardly ever took effect.
One factor that has diminished the effectiveness of previous approaches has been their inability to integrate the various models used for different aspects of the overall design problem.
As noted above the plurality of demands and approaches within the community advocating for maternal health and that focused on sexual and reproductive health and rights diminished the effectiveness of its response as its demands were fragmented.
In particular, the immediate paradoxical aftereffect, interpreted by us as a rebound effect, diminishes the effectiveness of sustained regulation.
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.
It diminishes the effectiveness of America's role as "honest broker" in the Mideast dispute.
